Multistage compressor

ABSTRACT

Refrigerant compressed by a first stage compression elements ( 30 ) run by a motor ( 20 ) is discharged in the closed container ( 10 ) via a silencer chamber ( 35 ) to cool the motor ( 20 ) before the refrigerant is led to a second stage compression element ( 40 ). The refrigerant is discharged from the second stage compression element ( 40 ) out of the compressor after it is further compressed in the second compression element ( 40 ). Thus, the motor ( 20 ) is cooled in a simple cooling mechanism during normal operation of the compressor.

FIELD OF INVENTION

[0001] The invention relates to a multistage compressor, and moreparticularly to a refrigeration system for use in such multistagecompressor.

BACKGROUND OF THE INVENTION

[0002] Compressors, particularly rotary compressors, have been used indifferent fields of engineering, especially in air conditioners andrefrigeration systems. These compressors mostly use chlorides containingrefrigerants such as R-22 (hereinafter referred to as Freon gas).

[0003] However, Freon gas is known to destroy the earth's ozone layerand its use is now legally regulated. Hence, extensive researches havebeen made for an alternative refrigerant that poses no such problem. Inthis regard, carbon dioxide is anticipated to be a good candidate.

[0004] A type of rotary compressor is known, which utilizes carbondioxide as a refrigerant (carbon dioxide will be hereinafter simplyreferred to as refrigerant unless it needs to be distinguished fromother refrigerants) in a multistage compressor incorporating multiplecompression elements.

[0005] Such multistage compressor comprises multiple compressionelements for sucking, compressing, and discharging the refrigerant; adrive element for driving these compression elements, and a housing foraccommodating the compression elements and the driving element.

[0006] Each of the multiple compression elements includes a roller whichis fitted on an eccentric cam formed integral with a rotary shaft of thedriving element and rolls on the inner wall of a cylinder. The spacebetween the roller and the cylinder is divided into a suction chamberand a compression chamber by a vane that abuts on the roller. Themultiple compression elements are adapted to sequentially performsuction, compression, and discharge of the refrigerant in multiplestages.

[0007] The driving element comprises an electric motor for rotating theshaft of the compression elements. These elements are all housed in aclosed container.

[0008] However, in such a conventional multistage compressor asmentioned above, the atmosphere surrounding the driving elements doesnot flow, so that heat generated by the driving element stays inside theclosed container, thereby raising the temperature of the drivingelement, which in turn hinders necessary compression of the refrigerant.This is a serious problem for apparatuses that utilize such compressor.

[0009] In other words, heat generated by the driving element must beradiated to the surroundings through the closed container, but it hasbecome increasingly difficult to install a heat removing fan forremoving heat from the compressor in a space around the compressor inorder to meet a recent commercial request for an ever compactcompressor.

[0010] Therefore, it has been an important matter in the design of acompressor to implement a mean for effectively radiating the heatgenerated by the driving element out of the closed container, hopefullywithout affecting the environment. A satisfactory solution, however, hasnot been found.

[0011] In order to overcome prior art problem as mentioned above, theinvention provides a multistage compressor capable of efficientlysuppressing heating of the driving element.

SUMMARY OF THE INVENTION

[0012] In accordance with one aspect of the invention, there is provideda multistage compressor having more than one compression elements forcompressing a refrigerant, and a driving element for driving saidcompression elements, said driving element and said compressing elementsaccommodated in an enclosed container, said multistage compressorcharacterized in that the refrigerant is adapted to cool the drivingelement after the refrigerant is discharged from one of the compressionelements and before it returns to the compression element in the nextstage.

[0013] Thus, with such a simple arrangement of the compressor, thetemperature rise of the driving element is efficiently suppressed.

[0014] Specifically, in one embodiment, a multistage compressor of theinvention includes a closed container, a driving element in the form ofan electric motor securely fixed in the upper section of the closedcontainer; a two-stage compression element, provided in the lowersection of the container, consisting of a first stage compressionelement and a second stage compression element which are driven byrespective eccentric cams mounted on the shaft of the motor,characterized in that

[0015] a connection tube is connected to the upper section of the closedcontainer which extends outwardly therefrom and returns to the inlet ofthe second stage compression element through the lower section of thecontainer;

[0016] the refrigerant taken in the first stage compression element iscompressed to an intermediate pressure (said refrigerant referred to asintermediate pressure gas) and discharged therefrom into the inner spaceof the closed container to cool the driving element;

[0017] the intermediate pressure gas is returned to the second stagecompression element through the connection tube; and

[0018] the intermediate pressure gas is further compressed to a highpressure and discharged therefrom by a second stage discharge tube.

[0019] Instead of directly discharging the intermediate pressure gasfrom the first stage compression element into the inner space of theclosed container, the gas may be alternatively discharged into the lowersection of the closed container through a first stage connection tubewhich is connected to the outlet of the first stage compression elementand extends once out of the container and returns to the lower sectionof the container.

[0020] Further, an additional refrigeration unit may be provided at anintermediate point of the first stage connection tube, or of the secondstage connection tube, to enhance heat radiation from the refrigerant,which helps increase the amount of the gas sucked into the second stagecompression element, thereby improving the compression efficiency.

BRIEF DESCRIPTION OF THE DRAWINGS

[0021]FIG. 1 is a cross sectional view of a preferred embodiment of atwo-stage rotary compressor according to the invention.

[0022]FIG. 2 is a partial cross sectional view of the two-stage rotarycompressor of FIG. 1.

[0023]FIG. 3 is a cross sectional view of another preferred embodimentof a two-stage rotary compressor according to the invention.

[0024]FIG. 4 is a cross sectional view of another preferred embodimentof a two-stage rotary compressor obtained by adding an extrarefrigeration unit to the compressor shown in FIG. 1.

[0025]FIG. 5 is a cross sectional view of another preferred embodimentof a two-stage rotary compressor obtained by adding an extrarefrigeration unit to the compressor shown in FIG. 2.

BEST MODE FOR CARRYING OUT THE INVENTION

[0026] Preferred embodiments of a two-stage rotary compressor accordingto the invention will now be described in detail with reference to theaccompanying drawings.

[0027] It should be understood, however, that the invention will not belimited to the embodiments described below, and that the invention maybe applied to a compressor having more than two stages.

[0028] As shown in FIG. 1, a rotary compressor includes a drivingelement in the form of an electric motor 20 and a first stagecompression element 30 and second stage compression element 40 mountedbelow the motor 20, all accommodated in a closed container 10, adaptedto compress in two stages carbon dioxide as a refrigerant.

[0029] Stored in the bottom section of the closed container 10 is alubricant 15 for lubricating sliding elements of the compressionelements 30 and 40.

[0030] The motor 20 consists of a stator 22 securely fixed on the closedcontainer 10 by shrunk fit, a rotor 23 securely mounted on a shaft 21which is rotatable with respect to the stator 22.

[0031] The first stage compression element 30 is provided at the inletthereof with a suction tube 11 for suction of the refrigerant from anexternal source. The refrigerant is compressed by the first stagecompression element 30 and discharged in the container 10 via a silencerchamber 35, as described in detail later.

[0032] The discharged refrigerant thus discharged flows past the motor20 and into a second stage connection tube 16 via an inlet 14 of theconnection tube provided in the upper section of the closed container10, and further into the second stage compression element 40 from thesuction tube 13 connected to the second stage connection tube 16.

[0033] The refrigerant is further compressed in the second stagecompression element 40 before it is discharged out of the compressorthrough a discharge tube 12.

[0034] Suction mechanism and compression mechanism of the first stagecompression element 30 and the second stage compression element 40 arethe same in structure: they are formed of respective cylinders 31 and41, respective rollers 33 and 43 installed inside the respectivecylinders 31 and 41.

[0035] Referring to FIG. 2, there is shown a side cross section of thefirst stage compression element 30.

[0036] As seen in FIGS. 1 and 2, the first stage compression element 30and second stage compression element 40 are formed of respective rollers33 and 43 which are in rotational engagement with respective cams 32 and42 formed on the rotary shaft 21, respective inner walls 31A and 41A ofthe cylinders 31 and 41, upper and lower support panels 36 and 46, andan intermediate partition panel 51.

[0037] Each of the upper and lower cams 32 and 42 is integrally formedon an extended section of the rotational shaft 21.

[0038] Rotatably fitted on the respective cams 32 and 42 are upper andlower rollers 33 and 43 such that the outer surfaces of the respectiverollers 33 and 43 abut and roll on the respective inner walls 31A and41A of the upper and lower cylinders 31 and 41.

[0039] The intermediate partition panel 51 is disposed between the upperand the lower cylinder 31 and 41 to separate them.

[0040] The intermediate panel 51 has a hole as indicated by a brokenline in FIG. 2. The hole is necessary for an eccentric cam 42 to passthrough it and the cylinders 31 and 41. The hole is coaxial with therotational shaft 21.

[0041] An upper and a lower cylinder spaces are formed on the oppositesides of the intermediate panel 51 by enclosing the spaces defined bythe outer surfaces of the respective rollers 33 and 43 and the innerwalls 31A and 41A of the respective cylinders 31 and 41 by means ofupper and lower support panels 36 and 46, respectively.

[0042] The upper and lower spaces are provided with respective upper andlower vanes 37 and 47 to partition the respective spaces. The vanes 37and 47 are slidably mounted in the respective radial guiding grooves 38and 48 formed in the respective cylinder walls of the upper and thelower cylinders 31 and 41, and biased by respective springs 39 and 49 soas to be in contact with the upper and lower rollers 33 and 43 at alltimes.

[0043] In order to carry out suction and discharge of the refrigerantgas into/out of the cylinder spaces, the cylinders are provided, on theopposite sides of the respective vanes 37 and 47, with upper and lowerinlets 31 a and 41 a and outlets 31 b and 41 b, thereby forming an upperand lower suction spaces 30A and 40A, and upper and lower dischargespaces 30B and 40B.

[0044] The upper support panel 36 and lower support panel 46 areprovided with respective discharge silencer chambers 35 and 45 which areappropriately communicated with the respective spaces 30B and 40B viadischarge valves (not shown) provided at the respective outlets 31 b and41 b.

[0045] The discharging valves are adapted to be opened when the pressurein the respective spaces 30B and 40B reaches a predetermined level.

[0046] In this arrangement, due to eccentric rotations of the respectiveeccentric rollers driven by the rotary shaft 21 of the motor 20, therefrigerant is sucked from an external source through the suction tube11 into the suction space 30A via the inlet 31 a of first stagecompression element 30.

[0047] The low pressure refrigerant gas is transported to, andcompressed in, the compression space 30B by the rolling motion of theroller 33 until its pressure reaches a prescribed intermediate pressure,when the valve provided at the outlet 31 b is opened to allow therefrigerant gas to be discharged into the inner space of the closedcontainer 10 through the silencer chamber 35.

[0048] The refrigerant discharged into the inner space of the closedcontainer 10 cools the motor 20 as it flows upward past the motor 20 tothe upper section of the closed container 10. The refrigerant then flowsinto the second stage connection tube 16 through the inlet 14 of theconnection tube and is led into the 40A via the inlet 41 a of the secondstage compression element 40 through the suction tube 11.

[0049] The sucked refrigerant is transported by the rolling motion ofthe roller 33 to the compression space 40B and further compressed fromthe intermediate pressure to a prescribed higher pressure, when thevalve provided at the outlet 41 b is opened to discharge the refrigerantout of the compressor via the silencer chamber 45 and through thedischarge tube 12.

[0050] In this way, the refrigerant discharged from the first stagecompression element 30 refrigerates the stator 22 and the rotor 23 whilepassing through the motor 20. This flow effectively suppresses thetemperature rise of the motor 20 even in cases where it is difficult toprovide an external heat radiating air passage on the closed container10 to remove heat from the driving element.

[0051] It might be thought that the refrigerant could be dischargedequally well from the compression element in the last stage into theclosed container to refrigerate the motor. To do so, however, it isnecessary to increase the maximum permissible pressure of the container,since carbon dioxide refrigerant generally has a much higher pressure inthe last stage as compared with R-22 refrigerants. Hence, this approachis not necessarily advantageous from a point of cost performance.

[0052] Although the invention has been described with a particularreference to a preferred embodiment in which the motor 20 isrefrigerated by the refrigerant compressed in the first stagecompression element 30 and discharged into the closed container 10 viathe silencer chamber 35, the invention is not limited to thisembodiment.

[0053] For example, a first stage connection tube 17 connecting theoutlet of the first stage compression element 30 to the lower section ofthe closed container 10 below the motor 20 may be provided so as to leadthe refrigerant compressed by the first stage compression element 30 outof the compressor once and then lead it to the closed container 10,thereby refrigerating the motor 20 before the refrigerant is returned tothe second stage connection tube 16, as shown in FIG. 3.

[0054] In this arrangement, the refrigerant effectively removes heatfrom the container and gets cooled outside the container as therefrigerant flows through the first stage connection tube 17 outside thecontainer, thereby further facilitating cooling of the motor 20.

[0055] By making the first stage connection tube 17 of a material havinga high thermal conductivity, cooling of the motor 20 may be enhanced.

[0056] In addition, a further refrigeration unit 18 or 19 may beconnected to the second stage connection tube 16 or the first stageconnection tube 17, as shown in FIGS. 4 and 5.

[0057] If the refrigeration unit 18 is connected to the second stageconnection tube 16, the amount of the refrigerant gas sucked into thesecond stage compression element 40 is increased, which will improve thecompression efficiency.

[0058] If, on the other hand, the refrigeration unit 18 is connected tothe first stage connection tube 17, cooling of the motor 20 is furtherenhanced, so that the amount of the refrigerant sucked into the secondstage compression element 40 is increased accordingly, which will alsoimprove the compression efficiency.

[0059] By making the second stage connection tube 16 and first stageconnection tube 17 of a metal having a high thermal conductivity such ascopper or aluminum, heat transfer from the motor 20 may be furtherincreased to enhance the cooling effect.

INDUSTRIAL UTILITY OF THE INVENTION

[0060] As described above, the invention provides a simple heat removingmechanism suitable for multistage compressors for use in different typesof refrigeration apparatuses and air conditioners.

[0061] A refrigerant efficiently cools the driving element of thecompressor between two compression stages as it is discharged into theclosed container after a first stage and returns to the second stage ofcompression, thereby solving the heat radiation problem pertinent toconventional compressors.

1. A multistage compressor including more than one compressing elementsfor compressing a refrigerant, and a driving element for driving saidcompression elements, said driving element and said compressing elementsaccommodated in an enclosed container, characterized in that saidrefrigerant is discharged from one compression element to cool saiddriving element before it returns to the compression element in the nextstage.
 2. The multistage compressor according to claim 1, characterizedin that said refrigerant discharged from said one compression elementand having cooled said driving element flows out of said closedcontainer and then returns to said compression element in the next stagethrough a connection tube connected to the upper section of said closedcontainer and inlet of said compression element in the next stage.
 3. Amultistage compressor including a closed container, a driving element inthe form of an electric motor securely fixed in the upper section ofsaid closed container, and a multiplicity of compression elementsprovided in the lower section of said closed container for carrying outsuction, compression and discharge of refrigerant in response to therotations of associated cams mounted on the shaft of said motor, saidcompressor characterized by: a first stage refrigerant suction tubeconnected to the compression element in the first stage, for introducinga low pressure refrigerant from a source outside said closed container;a last stage discharge tube connected to the outlet of the compressionelement in the last stage, said tube leading said refrigerant out ofsaid closed container; one compression element adapted to dischargetherefrom compressed refrigerant into the inner space of said closedcontainer to cool said driving element (said compression elementreferred to as cooling stage compression element); a first connectiontube that extends outwardly from the upper section of said closedcontainer and returns to the inlet of the compression element in thenext stage through the lower end of said closed container, said firstconnection tube leading said refrigerant that has cooled said drivingelement to said compression element in the next stage; and a secondconnection tube connected between the outlet of one compression elementand the compression element in next stage, except for said last stagecompression element and said cooling stage compression element, saidsecond connection tube configured to lead compressed refrigerant fromsaid one compression element to said compression element in next stage.4. A multistage compressor, including: a closed container, a drivingelement in the form of an electric motor securely fixed in the uppersection of said closed container, and a multiplicity of compressionelements provided in the lower section of said closed container forcarrying out suction, compression and discharge of refrigerant inresponse to the rotations of associated cams mounted on the shaft ofsaid motor, said compressor characterized by: a first stage refrigerantsuction tube connected to the compression element in the first stage,for introducing a low pressure refrigerant from a source outside saidclosed container; a last stage discharge tube connected to the outlet ofthe compression element in the last stage, said tube leading saidrefrigerant out of said closed container; one compression elementadapted to discharge therefrom compressed refrigerant into the innerspace of said closed container to cool said driving element (saidcompression element referred to as cooling stage compression element),said compression element connected at the outlet thereof to a connectiontube extending once out of said closed container and returning to thelower section of said closed container, a first connection tube thatextends outwardly from the upper section of said closed container andreturns to the inlet of the compression element in the next stagethrough the lower end of said closed container, said first connectiontube leading said refrigerant that has cooled said driving element tosaid compression element in the next stage; and a second connection tubeconnected between the outlet of one compression element and thecompression element in next stage, except for said last stagecompression element and said cooling stage compression element, saidsecond connection tube configured to lead compressed refrigerant fromsaid one compression element to said compression element in next stage.5. A multistage compressor, including a closed container; a drivingelement in the form of an electric motor securely fixed in the uppersection of said closed container; and a first stage and second stagecompression elements provided in the lower section of said closedcontainer for carrying out suction, compression and discharge ofrefrigerant in response to the rotations of associated upper and lowercams mounted on the shaft of said motor, said compressor characterizedby: a first stage refrigerant suction tube introduced from outside ofsaid closed container and connected to said first stage compressionelement; a connection tube that extends out of the upper section of saidclosed container and returns to the inlet of said second stagecompression element; and a second stage refrigerant discharge tubeconnected to the outlet of said second stage compression element andextending out of said closed container, wherein said low-pressurerefrigerant sucked into said first stage compression element throughsaid pre-stage suction tube is compressed to an intermediate pressure;said refrigerant compressed to the intermediate pressure is dischargedfrom the outlet of said first stage compression element into said closedcontainer, thereby cooling said driving element; said refrigerantdischarged into said closed container is returned to the inlet of saidsecond stage compression element through said connection tube; and thatsaid refrigerant sucked into said second stage compression element iscompressed to a high pressure in said second stage compression elementbefore said refrigerant is discharged by said second stage refrigerantdischarge tube out of said closed container.
 6. A multistage compressor,including a closed container, a driving element in the form of anelectric motor securely fixed in the upper section of said closedcontainer; and a first stage and second stage compression elementsprovided in the lower section of said closed container for carrying outsuction, compression and discharge of refrigerant in response to therotations of associated upper and lower cams mounted on the shaft ofsaid motor, said compressor characterized by: a first stage refrigerantsuction tube introduced from outside of said closed container andconnected to said first stage compression element; a first stageconnection tube connected to the outlet of said first stage compressionelement and extending once out of said closed container and returning tothe lower section of said closed container; a second stage connectiontube that extends out of the upper section of said closed container andreturns to the inlet of said second stage compression element; and asecond stage refrigerant discharge tube connected to the outlet of saidsecond stage compression element and extending out of said closedcontainer, wherein said low-pressure refrigerant sucked into saidpre-stage compression element through said pre-stage suction tube iscompressed to an intermediate pressure; said refrigerant compressed insaid first stage compression element is discharged from the outletthereof into said closed container via said first stage connection tube,thereby cooling said driving element; said refrigerant discharged intosaid closed container is returned to the inlet of said second stagecompression element through said second stage connection tube; and thatsaid refrigerant sucked into said second stage compression element iscompressed to a high pressure in said second stage compression elementbefore said refrigerant is discharged by said second stage refrigerantdischarge tube out of said closed container.
 7. The multistagecompressor according to claim 5 or 6, wherein each of said first stagecompression element and second stage compression element comprises:upper and lower eccentric cams formed on the shaft of said motor; tworollers rotatably fitted on said eccentric cams; two cylinders eachhaving an inner surface on which outer surface of said roller rotatablyabuts as said shaft is rotated; an intermediate partition panelseparating said cylinders; two support panels enclosing the upper andlower ends of the respective cylinders; two vanes, one for eachcylinders for partitioning a respective closed space defined by therespective outer surface of said roller, inner surface of said cylinder,said support panel, and said intermediate panel, into a suction spaceand a discharge space; two inlets, one for each cylinder, for suckingrefrigerant into said suction spaces; two outlets, one for eachcylinder, for discharging compressed refrigerant out of the respectivedischarge spaces, and wherein the refrigerant sucked into the respectivedischarging spaces via said respective inlets is compressed in therespective discharge spaces and discharged from the respective outletsin response to the rotation of said shaft.
 8. The multistage compressoraccording to claim 5 or 6, wherein a refrigeration unit is provided atan intermediate point of either one of said first stage and second stageconnection tubes.